This invention relates to a punch press, more particularly to a punch press including a plurality of punch pressing units which have a common driving crankshaft with several angularly spaced eccentric sections.
In this art, a punch press includes several punch pressing units, each of which consists of a punch and a die set. Referring to FIG. 1, an earlier conventional punch press includes a frame A1, a crankshaft A2, a coupler A3 connected to the eccentric portion of the crankshaft A2, a ram A4 with several punches A5, and several die sets A6. The punches A5 effect different forging operations. Because of the difficulty in registering the center of gravity of the ram A4 with the coupler A3 and the rather large pressure created by the ram A4, stress concentration and unbalance take place on the ram A4, resulting in deformity and wear of said ram A4. Consequently, the precision and lifetime of the punch press are reduced.
Referring to FIG. 2, to minimize the unbalance of the punch press shown in FIG. 1, two aligned couplers B5 connect a ram B1 to the eccentric portion of a crankshaft B4. However, the unbalance condition will still occur in the punch press due to the fact that punches B2 effect different forging operations and apply pressures of different magnitudes to dies B3.
Several workpiece gripping units are provided on the punch presses shown in FIGS. 1, 2 so as to move workpieces between the dies A6, B3. When one of the gripping units malfunctions, although the malfunctioned gripping unit can be immediately stopped, there is still a high degree of unbalance during the punch pressing process. This unbalance damages the parts of the punch press. Furthermore, because all of the punches A5, B2 effect the forging operation at the same time, it is necessary to output a very large amount of power to the ram A4, B1. As a result, the lifetime of the crankshaft A2, B4 is reduced.
Referring to FIG. 3, a conventional workpiece gripping unit includes a carrier (C) with an enlarged block C1 disposed at the lower end thereof. The block C1 has a lower end surface C2 with two aligned retaining grooves C3, C4, and two opposite side surfaces C5 with threaded holes C6. Two adjustment bolts C7 extend through the threaded holes C6 of the block C1 to press against two curved spring sheets E1, E2, which push two gripping arms D1, D2 against the partition C8 of the block C1. Each of the gripping arms D1, D2 has a gripping notch D11, D21 formed in the inward side surface thereof, and a retaining notch D12, D22 formed in the outward side surface thereof. The gripping notches D11, D21 of the gripping arms D1, D2 define an accommodating space in which a workpiece can be clamped tightly between the gripping arms D1, D2. The upper ends E11, E21 of the spring sheets E1, E2 are inserted into the retaining notches D12, D22 of the gripping arms D1, D2. This gripping unit suffers from the following disadvantages:
(1) The retaining grooves C3, C4 of the block C1 must be sufficiently large to accommodate both the upper end portions of the gripping arms D1, D2 and the spring sheets E1, E2. Accordingly, it is necessary to increase the volume of the gripping unit. PA1 (2) Because the spring sheets E1, E2 are entirely accommodated in the retaining grooves C3, C4 of the block C1, the outward movement of the lower ends of the gripping arms D1, D2 is limited. Thus, the gripping arms D1, D2 cannot clamp a workpiece of large size therebetween. PA1 (3) It is understood in the machining field that the formation of the retaining grooves C3, C4 in the block C1 is time-consuming. For example, the block C1 is first drilled to form circular grooves and is subsequently machined to form rectangular grooves.